Prepare public open-source release

[STFQ]

Summary

• Remove product activation and issuer logic for the public open-source build
• Add README, security guidance, contribution docs, attribution, and AGENTS.md
• Add verified Windows build, packaging, and tag-triggered release automation
• Add repository search description and Topics

Validation

• npm run build
• cargo test --manifest-path src-tauri/Cargo.toml --features custom-protocol
• npm run build:desktop-client